Cementitious grout compositions are generally known. The term “cementitious”, as used herein, means a material which comprises hydraulic cement, that is, a calcium alumino-silicate, which when mixed with liquid water, will set to form a hard resultant product. The most common type of such cementitious material is known as “Portland cement” and, for the purposes of this disclosure, is what is meant by the term “cementitious material”. While Portland cement materials are most common, other materials such as a relatively high-alumina cement material, a granulated blast furnace slag cement and slag/Portland cement blends are also know. Additionally, it is known that cementitious materials may contain other materials, which are not in themselves cementitious, but which can make a contribution to the setting of the final product. Examples of these added materials are the various natural and artificial pozzolans.
The need for grout in micro-trench applications is also known. Micro-trenching is a process where a trench is cut in the ground, typically using a trenching machine that is capable of cutting through cement, asphalt, earth, etc. Such micro-trenches are useful in embedding cables, conduits, pipes and other articles in the ground such as when running new fiber optic cables in an existing infrastructure. The term “micro-trench” generally refers to the fact that the trench created in the ground has a depth of greater than a few inches and also has at least some width. Once a micro-trench has been created, it is possible to insert a conduit, such as a plastic sleeve created continuously or having coupled sections running a given length, into the micro-trench. Generally, once the micro-trench is created and the conduit put in place, a grout material can be used to fill the micro-trench partially or completely to fill the hole and secure the conduit.
As a grout material, Portland cement-blended grout products have disadvantages with respect to filing a micro-trench as the produced fluids have a relatively high water to cement ratio mixtures. This results in relatively significant shrinkage amounts due to the high temperature calcium-monoxide CaO and calcium-carbon monoxide CaCO reactions. This shrinkage leads to relatively significant surface defects and to a relatively high amount of consolidation both of which are too significant for success as a micro-trench grout application. While the strength performance could be improved, the relatively high heat of hydration causes difficult workability in the field particularly in summer-time temperatures (above 80 degrees Fahrenheit). Additionally, the Portland-based cement-blended grout products are typically not sufficiently liquid enough (thin or fluid), which leads to bridging of the material across the trench and/or around any structures placed in the micro-trench thereby causing poor hydration and poor set properties due to voids and other imperfections in the cured grout. This is particularly a concern when hydration temperatures are relatively high, above 100 degrees Fahrenheit. Accordingly, overall poor consolidation and other issues with Portland cement-based grout products are too significant to consider it a viable option in a micro-trench application.
Other cementitious grout materials are similarly insufficient. An exemplary cementitious grout material is disclosed in U.S. Pat. No. 5,536,610, the entire contents of which are incorporated herein by reference, and as shown, the cementitious grout includes a fly ash material. The term “fly ash” is defined in Standard Specification C 618 of the American Society for Testing and Materials (ASTM) as a “finely divided residue that results from the combustion of ground or powdered coal”. ASTM C 618 (the contents of which are incorporated herein by reference) defines two distinct types of fly ash, Class F and Class C. Class F is obtained from the combustion of anthracite or bituminous coal and is being more common than the Class C, which is obtained from the combustion of sub-bituminous coal or lignite. One characterizing feature of Class C fly ash is its higher calcium-containing material content, expressed as lime content, and as stated by ASTM C 618 as often “higher than 10%”. The use of fly ash in cementitious grout compositions confers useful properties such as enhanced final strength and durability and reduced permeability. However, fly ash also confers low early strength, which is disadvantageous in many applications, and also retards the set time.
A mixture of bentonite clay and water has also been used to create a grout mixture for use in a bore hole or other ground application. Bentonite is an adsorbent, generally made from impure clay which was formed from volcanic ash that has weathered. The component make up of bentonite varies widely depending upon the geographic region and the constituent parts that make up the particular bentonite material as is known. Accordingly, there are several primary different types of bentonite. The names of the types of bentonite typically depend on the dominant element of the bentonite, such as potassium (K), sodium (Na), calcium (Ca), and aluminum (Al).
However, it is also generally known that bentonite/water grout mixtures lead to a resultant product having low strength gain during the setting process and 60-70% by volume loss of fluid due to shrinkage. Because bentonite material does not hydrate, bentonite minerals settle out of the fluid rapidly leaving large volumes of bleed water on the surface of the grout composition when located in a hole or trench. Due to significant consolidation of bentonite grout mixtures, if a level finished ground is desired, then the amount of back fill necessary to fill the hole greatly increases. For example, in a micro-trench application, the addition of an asphaltic sealer on top of the set bentonite/water mixture is generally known. However, the greater the consolidation of the grout material, the greater the amount of asphaltic sealer needed to obtain a flat finished surface, which is a requirement for pavement applications. Also, if the asphaltic sealer (generally applied at a relatively high temperature) is applied too quickly after setting of the bentonite grout mixture, it will result in the boiling of water which collects on top of the bentonite-based grout and leads to the complete dehydration of the bentonite/water mixtures ultimately leading to complete failure of the grout. Accordingly, bentonite/water mixtures are not considered a viable option for use in micro-trench applications.
While it is also known to use a graphite-based grout blended with water, this solution has proven not a viable option for micro-trenching due to the blends shrinkage and consolidation. Graphite-based grout blended with water compositions also demonstrate significant bridging of the material when used in a micro-trench application as it does not flow effectively into the micro-trench. Finally, the cost of graphite-based grout blended with water is also a major drawback. The graphite-based grout bagged material is estimated to cost up to ninety dollars (US $90) per fifty pound (50#) bag. It is anticipated that at this cost level, the product would likely meet with nearly no significant market acceptance.
In another example similar to the above mixtures, it is also known to use four (4) bags of silica sand added to one (1) bag of bentonite clay for addition with a water reducing admixture added to one (1) bag of a Portland cement to also prepare a cementitious grout mixture. This mixture is known for use as a geothermal grout in a bore hole in the ground. This mixture is not suitable for micro-trench applications.
Thus, given the relatively high ratio of the micro-trench and the potential applications, such as in roadways where there is a great deal of load requirements, to date, no acceptable grout has been developed that will adequately perform for this application. In particular, known grout mixtures are difficult to maintain flowability while placing, and have significant drawbacks when attempting to pump through drilling contractors on-board mud pumps. While some of these concerns might be addressed through the use of additional pump equipment for placement of the mixed grout, the micro-trench and conduit remain subject to bridging. It is known that some laborers are accustomed to adding extra water to grout compositions in an effort to make the grout mixture flow better. However, the extra water damages the grout composition and its ability to properly cure leading to significantly poor and unacceptable performance of the installed system. For a bentonite grout, the greater the added water for flowability, the higher level of shrinkage and cracking that will occur. These cracks and fissures create air gaps along surfaces of the grout and its interface with the conduit allowing ground water to flow into and fill the voids and further degrade the performance.